Variable speed wiper-type control switch



y v15, 1969 a. H. MATTHEWS 3,456,229

VARIABLE SPEED WIPER-TYPE CONTROL SWITCH Filed May a, 1967 2 Sheets-8haet l y 5, 969 B.'H. MATTHEWS 3,456,229

VARIABLE SPEED WII'TJR TYPE CONTROL SWITCH Filed May a, 1967 2 Sheets-Shet :2

j? i l INVENTOR.

United States Patent US. 'Cl. 338198 1 Claim ABSTRACT OF THE DISCLOSURE The speed control switch is adapted for mounting in an electrically-powered rotary tool, such as a food mixer of the hand type which is adapted to be manually maneuvered during its operation, and which switch has an externally accessible actuating lever member for selectively varying the speed of the electric motor of the tool. The lever is adapted to actuate a wiper-type electrically conductive contact element which bridges a rheostat bar and a stationary contact member. Movement of the contact element relative to the rheostat bar varies the current flow to the motor to vary the speed of the motor, with the movable contact element being movable from an off position wherein it is spaced from the stationary contact member, to a fully on position wherein the rheostat bar is bypassed. The switch is of miniaturized construction and includes a silicon-controlled rectifier and an RC. time constant circuit, all disposed in a compact arrangement for ready mounting in a tool.

This invention relates in general to a compact electrical switch for a hand-operated power tool, such as, for instance, a portable food mixer, and more particularly to a continuousl variable speed control wiper switch of compact construction for selectively varying the speed of the electric motor of the tool.

There are numerous switches known in the art for controlling the speed of an electric motor of a hand type tool. However such switches generally have predetermined speed stations, and thus are not expeditiously adjustable for smoothly adjusting the motor speed, and moreover are usually unduly complex and bulky, thus compounding the problems of mounting the switch on the tool.

The present invention provides a compact, continuously variable speed control wiper-type switch which includes an electrically conductive wiper contact member bridging a rheostat bar and a stationary contact bar, for selectively varying the magnitude of electrical energy to the motor and thus provide for smoothly varying the speed of the electric motor.

Accordingly, an object of the present invention is to provide an electrically-driven rotary tool having a novel variable speed wiper-type switch mounted thereon for selectively controlling the speed of the tool.

Another object of the invention is to provide a novel variable speed switch for an electric motor.

A further object of the invention is to provide a switch of the latter-mentioned type which is compact, economically constructed, and capable of being mass produced.

Another object of the invention is to provide a variable speed control switch having an electrically conducting wiper contact element pivoted to the switch body with one contact point on the wiper element being adapted for engagement with a rheostat bar and with another contact point on the wiper element being adapted for engagement with a stationary electrically conducting contact bar on the switch body, with such wiper element bridging the rheostat bar and the stationary contact bar, and with the wiper element in one position being moved 3,456,229 Patented July 15, 1969 out of engagement with the stationary contact bar for thus breaking the switch circuit, and in another position shorting out the rheostat bar while bridging the stationary contact bar to be in a completely on position.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a generally diagrammatic, perspective illustration of a food mixer embodying the speed control switch of the present invention;

FIGURE 2 is an enlarged side elevational view of the speed control switch of the invention with the control lever thereof being shown in full lines in an off position;

FIGURE 3 is a side elevational view of the switch of FIGURE 2 taken from the opposite side thereof and with the control lever being in the same position as that of FIGURE 2;

FIGURE 4 is an end elevational view of the FIGURE 2 switch taken generally along the plane of line 4-4 of FIGURE 2 looking in the direction of the arrows;

FIGURE 5 is a top plan view of the FIGURE 2 switch;

FIGURE 6 is a view generally similar to FIGURE 2 but illustrating the control handle moved to a position for energizing the electric motor of the tool;

FIGURE 7 is an enlarged fragmentary sectional view taken generally along the plane of line 7-7 of FIGURE 2 looking in the direction of the arrows, and illustrating in particular the wiper contact element;

FIGURE 8 is an enlarged fragmentary sectional view taken generally along the plane of line 8--8 of FIGURE 6 looking in the direction of the arrows;

FIGURE 9 is an enlarged fragmentary view similar to FIGURE 3, but with the cover of the switch housing removed to illustrate some of the component parts of the switch circuit;

FIGURE 10 is an enlarged plan view of the insulating connector member which couples the switch lever to the contact element of the switch for actuation of the contact element; and

FIGURE 11 is a schematic illustration of the variable speed control switch coupled to a series motor of, for instance, the power tool illustrated in FIGURE 1, for selectively controlling the speed of the tool.

Referring now again to the drawings there is shown an appliance, such as a portable food mixer 10 embodying the variable speed control switch S of the invention. The switch in the embodiment illustrated comprises a body 14 which ma be formed of a suitable electrical insulating material, such as for instance, plastic, and with such body portion 14 comprising a plate-like mounting portion 14a which is adapted for attachment in the frame 16 of the hand tool or food mixer 10, and an enclosure or housing portion 14b secured to the mounting portion 14a. Enclosure portion is adapted to receive therein various component parts of the switch circuit for varying the speed of the electric motor of the tool as will be hereinafter described.

As can be seen in FIGURE 1, the switch S is adapted for mounting in the frame 16 of the tool so that the control lever member 18 of the switch projects through a slot 20 in the frame handle, for convenient accessibility to the fingers of the operator, while the tool is manually held in the hand of the operator.

The lever 18 may comprise an upper shank portion 18a having a forked outer end, which is adapted to receive thereover in mounted relation a cap-like member 19 (FIG- URE 3) which cap is adapted to project through the aforementloned slot in the tool handle portion. Shank portion 18a of the lever, in the embodiment illustrated, is generally coplanar with the plane of mounting portion 14a of the switch body and is connected by an offset portion 22 of the lever with a foot portion 24.

Foot portion 24 has an opening therethrough receiving a pivot 24a thereby pivoting the lever member 18 to the switch body. The foot portion preferably has tabs 25 thereon which project therefrom into complementary slots 26 in insulating spacer member 28 (FIGURE The insulating member 28 separates and electrically insulates the lever 18 from the wiper-type contact member 30 which is adapted for securement to the insulating member, the latter being secured by the aforementioned tabs 25 to the lever 18. The insulating member 28 may be formed of any suitable insulating material such as, for instance, a paper base phenolic laminate.

Contact member 30 is of the wiper-type and comprises a base portion 30a which includes generally upstanding tabs 31 (FIGURE 7) thereon coacting with Slots 31a in the insulating member 28, and an arched body portion 32 extending from the base portion 30a and having contact points 33 and 34 formed thereon, as can be best seen in FIGURES 7 and 8. Contact point 33 is formed on partially-severed portion 36 of contact member 30 while contact point 34 is formed adjacent the distal end of member 30.

Underlying contact member 30 and secured to the outer side of mounting portion 14a is a rheostat bar 38. Rheostat bar 38 may comprise a base formed of electrical insulating material, such as, for instance, Bakelite, covered on the exterior surface thereof with a carbon layer forming a preselected value of resistance. Disposed adjacent one end of the rheostat bar and in electrically-communicating relation therewith is an electrically-conducting terminal portion 40, which may be of the strap-like configuration illustrated secured to the mounting portion 14a of the switch body. As will be understood, when the control lever 18 is disposed in the full on position 42 (FIGURE 2), contact point 33 on contact member 30 will be in engagement with terminal 40, while contact point 34 on contact member 30 will be in engagement with the electrically conducting stationary contact bar and heat sink 44 secured to the mounting portion 14a in spaced relationship to rheostat bar 38, thus bypassing the rheostat bar.

In every other position of wiper member 30 from t e full on position 42 and up to (but not including) the off position (FIGURE 2) of the lever 18, the contact point 33 engages the rheostat bar at a selected distance from the terminal 40, while the contact point 34 also engages stationary contact bar 44. In the off position of the lever 18 shown in FIGURE 2, the contact point 34 on contact member 30 is moved completely off the stationary contact bar 44, due in part to the cutaway portion 46 (FIGURE 2) thereof, thus isolating stationary contact bar 44 from electrical communication with the rheostat bar 38 and opening the switch circuit.

In this connection the switch body may be provided with a cam 48 thereon which is adapted for engagement with the underside of the arched contact member 30 to actually force or raise the contact point 34 upwardly in spaced elevation with respect to the plane of the stationary contact bar 44, to positively insure that no arcing can occur between contact member 30 and the stationary bar 44 in the off position of the switch. It will be understood that the arched configuration of contact member 30 urges the contact points 33 and 34 into forced or tensioned engagement with respectively the rheostat bar 38 and the stationary contact bar 44, and thus the lever 18, while it is readily movable upon application of force by the operators finger, remains in whatever position the lever 18 is placed without any tendency to move from such selected position. Stop 49 may be provided for limiting the pivotal movement of contact member 30 in the off position.

Referring now to FIGURES 9 and 11, it will be seen that in FIGURE 9, the cover member 50 (FIGURES .3 and 4) has been removed from the enclosure portion 14b of the switch body, showing other of the component parts of the switch circuit. In actual practice, enclosure 14b maybe filled with an insulating material such as a rubberized material inserted in liquid form which then hardens. As shown in FIGURE 11, the armature 51 of the universal motor of tool 10 is seen to be connected at one end to a suitable alternating current source, such as volts, by line conductor 52, the opposite side of the source of current being connected by line conductor 54 to switch terminal 55, which is connected to stationary contact bar 44 of the switch. One end of the field winding F of the motor is likewise seen to be connected by conductor 58 to switch terminal 59 (FIGURE 3) to thereby connect such switch with the motor and across the aforesaid 110 volt A.C.

source.

The universal type of motor is designed to operate in either alternating or direct current circuits and the instant variable speed control switch when used in an alternating current circuit is adapted to deliver discreet pulses or slugs of energy of predetermined quantity and cyclic rate to the motor. Inasmuch as the speed of the motor depends upon the energizing rate and current, the motor speed will correspondingly change in proportion thereto.

The switch circuit in its present embodiment is seen to include a silicon-controlled rectifier 60 preferably of conventional solid state design, and which is seen to have an anode, cathode, and gate electrodes 60a, 60b and 600 respectively. The aforementioned switch terminal 59 is seen to be connected to the anode electrode 60:: and the cathode electrode 60 h of the rectifier is connected to the stationary contact bar 44 via the wiper contact member 30, thus connecting the anode-cathode circuit of the rectifier in series with the field and armature of the universal motor and across the 110 volt A.C. source.

The gate electrode 600 of the rectifier is connected to one electrode of a neon lamp 64 with the opposite electrode of the lamp being connected via conductor 66 to the junction of the connection between the wiper contact member 30 and capacitor 68. The rheostat bar 38 is preferably connected via the aforementioned terminal strap 40 to a trimmer resistor 70 (of conventional type) which provides an adjustable means for limiting the current. The capacitor 68 is connected across the cathodegate circuit of the silicon-controlled rectifier 60 in series with the neon lamp 64.

It will be seen that with the instant arrangement, as the switch lever 18 is moved from its otf" position, the contact point 34 on contact member 30 will engage the stationary contact plate 44, thereby closing the open switch circuit to thereby connect the motor and control switch across the alternating current source. Movement of the lever 18 from the ob. position with the contact point 33 engaging the rheostat bar and contact point 34 engaging the stationary contact bar will vary the speed of the motor as dependent upon the position of the contact member 30 with respect to the bar 38. When the contact point 33 engages the terminal contact strap 44, the rheostat contact bar is bypassed.

From the foregoing discussion and accompanying drawings it will be seen that the invention provides a novel, variable-speed wiper-type control switch, including a rheostat bar and a stationary bar, with a contact member adapted to bridgethe bars for selectively and smoothly controlling the speed of an associated motor. The invention also provides a switch of the latter-mentioned type which is extremely compact and miniaturized for convenient assembly into a hand-operated tool, such as, for instance, a portable mixer.

The terms and expressions which have been used are used as terms of description and not of limitation and there is no intention in the use of such terms and expressions of excluding any equivalents of any of the features shown or described, or portions thereof, and it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. In a compact electrical speed control switch comprising a body portion, at least a pair of stationary elec- 5 trical conducting means on said body portion, resistance means mounted on said body portion extending between said stationary conducting means and including an arcuate plate formed of insulating material and coated with a layer of carbon to define a predetermined resistance, an electrical conducting contactor pivoted to said body portion and adapted for wiping engagement with said conducting means and said resistance means, the center of curvature of said arcuate plate being generally coincident with the pivotal axis of said contactor, the positional engagement of said contactor with respect to said resistance means being adapted to vary the magnitude of electrical energy to a motor adapted to be connected in circuit with said conducting means so as to vary the speed of the motor, terminal contact means coacting in electrical conducting relation with said resistance means and effective when engaged by said con- References Cited UNITED STATES PATENTS 2,504,873 4/1950 Porter 338196 X 2,987,636 6/1961 Jepson 200157 X 3,324,437 6/1967 Heller 338174 X 3,255,319 6/1966 Paine 20011.11

ROBERT K. SCHAEFER, Primary Examiner H. J. HOHAUSER, Assistant Examiner 

